Variable resistor



m Z9, E95? A. J. MQSEFZ VARIABLE RESISTOR Filed Nov. 16, 1953 Gv mM.

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ww @RMX A T TOR/VE V nited States Patent O VARIABLE RESISTOR Arthur J. Moser, San Juan, Puerto Rico, assignor, by

mesne assignments, to International Resistance Company, Philadelphia, Pa., a corporation of Delaware Application November 16, 1953, Serial No. 392,377

3 Claims. (Cl. 20L-S3) This invention relates to electric switches and more particularly to multiple pole electric switches having a plurality of electrical contactors.

In conventional switches having contactors controlling the operation of a variety of electrical components, the components and the connections between the contactors and the components are exposed to atmospheric effects such as temperature and humidity; and are also exposed to mechanical shock. In addition, many conventional switches contain mechanical elements made of conductive materials properly forming no part of the electrical circuit which the switches serve, but presenting a source of potential trouble due to humidity causing short circuits.

The present invention overcomes the above disadvantages by providing an electric switch in which the contactors and the components which they control are enclosed in an insulating plastic body, and the number of conductive mechanical elements is considerably reduced.

The present invention provides a switch which is shock resistant and which protects the components it controls from temperature fluctuation and humidity. In addition, the smooth surface on which the conductor slides keeps the Contact surface of the conductor polished clean, and allows the conductor to make and break Contact with the contactors with no tripping which results in an extremely low switch noise level. The use of a portion of the plastic body as part of the detent arrangement further reduces the amount of conductive material which forms no part of the electrical circuit.

The present invention contemplates a multiple pole electric switch in which the electrical contactors and the electrical components to which they are connected are embedded in an insulating plastic body. The plastic body is provided with a smooth surface in which the contactors are embedded with their exposed surfaces substantially ush with the smooth surface. A contact arm having a conductor is fastened to the body so that the arm is movable with respect to the body. As the arm is moved the conductor successively comes in contact with each of the contactors. A series of depressions is cast in the surface of the body along the direction of movement of the conductor. Preferably, a spring-loaded detent is fastened to the arm and adapted to rest successively in each of the depressions as the arm is moved.

These and other aspects of the invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawing in which:

Fig. 1 is an elevation in partial section of an embodiment of the invention as employed in the construction of a potentiometer, and provided with a protective cover;

Fig. 2 is a bottom view of the device shown in Fig. 1 with the cover removed;

Fig. 3 is a sectional elevation taken on line 3 3 of Fig. 2 with the control knob removed; and

Fig. 4 is a wiring diagram of the circuit of the potentiometer of Fig. 1.

The switching device illustrated in the accompanying drawing is adapted to serve as a potentiometer, but the same general construction can be employed for any type of circuit in which a multiple pole switch is employed.

Referring to the drawing, a body 10 made from a liquid polyester plastic resin by conventional molding methods for resins that solidify upon polymerization is formed in the shape of a cylinder having a diameter slightly greater than its length. The body is an electrical insulator and is formed around a vertical tubular bearing sleeve 11 which provides a coaxial bore 12 through the body. The sleeve is knurled externally to increase bonding between it and the plastic body. The sleeve is approximately ush with the lower end surface of the body. The upper end of the sleeve projects above the smooth upper surface of the body.

The periphery of the lower end surface is formed with a smooth annular projection 13 coaxial with the bore, leaving an annular recessed portion 14 between the sleeve and the annular projection. A series of contactors 15, 15A-15T is embedded in the annular projection on a circular arc and at equally spaced intervals. The exposed surfaces of the contactors are flush with the smooth surface of the annular projection. An annular conductive ring 16 coaxial with the bore is embedded in the lower end of the plastic body adjacent the inner surface of the annular projection. The lower surface of the annular conductive ring is flush with the lower surface of the annular projection. A series of ridges 17 extending radially with respect to the bore axis are formed integrally on the annular recessed portion of the body, providing a series of depressions in that surface. A radially extending, wedge-shaped projection 18 is formed integrally on the annular recessed portion of the body and its lower surface is ush with that of the conductive ring and the annular projection on the lower end of the body.

A circular end-plate 19 having a coaxial bore 20 of the same diameter as the O. D. of the sleeve is slipped over the upper end of the bearing sleeve to fit snugly against the plastic body. A portion 21 of the bore in the endplate remote from the plastic body is tapered to provide a bore of increased diameter near the exposed surface of the end-plate. The bearing sleeve is ared at 22 adjacent the tapered part of the end-plate bore to hold the end-plate against the body. The end-plate is provided with threaded holes 23, 23A for mounting the switch on a control panel.

Two oil-containing porous bushings 24, 25 are pressed into each end of the bearing sleeve, respectively. A shaft 26 is journaled through the bushings so that it extends beyond each end of the plastic body. A washer 27 is disposed over the shaft to ride on the bushing at the end of the plastic body having the end-plate. A retaining G-washer 28 is fitted into an annular groove 29 provided in the shaft intermediate the ends of the shaft and bears against the washer riding on the bushing. The lower end of the shaft is provided with a at surface 30 extending in the direction of the shaft axis.

An elongated plastic arm 31 is provided with a bushing 32 molded into one end of the arm to forni a transverse bore 33 through that end. rIhe external surface of bushing 32 is knurled to provide for effective bonding between the plastic arm and the bushing. The arm is mounted on the lower end of the shaft by means of the bus-hing being slipped over the shaft. The bushing projects slightly above the upper surface of the arm and bears against a washer 34 on the lower end of the shaft and bearing against the lower end of lower oilite bushing 25. The arm is rigidly attached to the shaft by means of a set screw 35 threaded longitudinally through the end of the arm to bear against the flat surface of the shaft. The over-all length of the plastic arm is such that the end of the arm Vremote-from the shaft extends almost to the periphery of the body.

Six elongated conductive strips 36, 37, 3S, 39, 40, 4l stacked one on the other are soldered together at one end. The soldered endof the strips is embedded in the end of the plastic arm remote from the shaft so as to form a cantilever leaf spring arrangement pivoting about a horizontal axis and urging its free end in an upward direction. The bottom three elongated strips are slightly longer than the top three and are bent upwardly at their free end to Vforni a brush arrangement making successive electrical contact with the contactors as the arm is rotated. The top three strips are bent upwardly at their free ends to form a brush arrangement making continuous Contact with the annular conductive ring as the Varm is rotated.

A knurled detent sleeve 42 is transversely embedded in the plastic arm so that the lower end of the sleeve is ush with the upper surface of the arm and the upper end of the detent Sleeve projects above the upper surface of the arm into the annular recessed portion of the body. The'upper end of the detent sleeve engages the wedgeshaped projection on the body and prevents the arm from being rotated 360. The lower portion of the detent sleeve is threaded and provided with a screw 43 which bears against a detent compression spring 44 provided above it, which in turn bears against a detent ball 45 positioned in the upper end of the detent sleeve. This lball is adapted to rest successively in each of the depressions formed in the plastic body as the arm is rotated. The spring loading on the detent ball is controlled by the position of the screw.

A conventional control knob 46 is attached rto the upper end of the shaft to facilitate rotation of the arm for switch operation.

A plurality of serially connected resistors 47, 47A-47T are embedded in the plastic body. Each contactor is connected to the series of resistors as shown in the wiring diagram of Fig. 4. A vertical plate of insulating material 48 having three vertically disposed terminal posts 49, 50, 51 is embedded in the side of the plastic body and each of the terminals is connected by wires embedded Vin the plastic body, as shown in the wiring diagram of Fig. 4. A vertical elongated projection 52 is formed integrally with the body around the base of the terminal posts.

A cover 53 in the shape of a cylinder, open at one end and having a vertical notch in the upper portion of its side wall to accommodate the terminals, is adapted to slip over the lower end of the plastic body and be held by friction.

The. plastic parts of the switch arrangement just described are formed by conventional plastic molding methods. However, it has been found that a switch having exceedingly quiet operation and long life can be obtained if care is taken to insure that the exposed surfaces of the contactors are flush with the adjacent body surface. To this end, the surface of the body containing the contactors is Vfaced off in a lathe and then hand polished to provide an extremely smooth surface.

A switch constructed in accordance with this invention provides the advantage that the electrical components served by the switch and the connections between the contactors and the components are completely embedded in a tough plastic body. This provides protection against shock, moisture and temperature fluctuations. This type of switch alsoprovides a smooth, flat contact surface which is easily cleaned and has an exceptionally long life. In addition, the contact brushes slide over the contactors without any tripping and provide an extremely low switch noise level. The smooth surface on which the conductor slides to maize contact with the contactors also burnishes the Contact surface of the conductor as the conductor is rotated, thus ensuring constant contact resistance. The detent arrangement molded in the plastic body provides positive means for maintaining a desired switch operating position without any danger of providing a short-circuited path.

l claim:

1. A variable resistor comprising the combination of a .resistance element, a body of an insulating thermosetting plastic completely surrounding the resistance element and comprising the sole support therefore, said body having a flat surface, a plurality of spaced conductive contactors embedded in said ilat surface of said body with a surface of each of said contactors being flush with said body surface, said contactors being arranged in an arc and connected to the resistance element at spaced points therealong, a plurality of spaced indentations in said flat surface of the body arranged in an arc co-axial with the arc of said contactors, a shaft rotatably supported by said body, an arm of insulating material fastened to said shaft adjacent said body surface, a conductor attached to said arm and adapted to successively contact the contactors upon rotation of said arm, and a spring loaded detent fastened to said arm and adapted to successively rest in each of the indentations as the arm rotates.

2. A variable resistor comprising the combination of a body of an insulating thermosetting plastic having a at surface and a hole extending through said body and opening at said surface, a resistanceV element completely embedded in said body which comprises the sole support therefore, a plurality of spaced conductive contactors embedded in said ilat surface with a surface of each of said contactors being flush with said body surface, said contactors being arranged in an arc co-axial with said hole and connected to the resistance element at spaced points ,therealong, a plurality of indentations in said at body surface arranged in an arc co-axiaI with said hole, a shaft extending through said hole and rotatably supported by said body, an arm of insulating material fastened to said shaft adjacent said body surface, a conductor attached to said arm and adapted to successively Contact the contactors upon rotation of said arm and a spring loaded detent fastened to said arm and adapted to successively rest in each of the indentations as the arm rotates.

3. The combination as set forth in claim 2 in which there are at least one indentation for each contactor and the indentations are so arranged that when the detent is seated in an indentation the conductor contacts one of the contactors.

References Cited in the file of this patent UNITED STATES PATENTS 673,108 Berresford Apr. 30, 1901 698,200 Hinds Apr. 22, 1902 910,835 Macy Jan. 26, 1909 1,087,453 Manross Feb. 17, 1914 1,768,299 Simon lune 24, 1930 2,034,866 Harvey Mar. 24, 1936 2,163,069 Stringer June 20, 1939 2,206,882 Davis July 9, 1940 2,222,564 Henry Nov. 19, 1940 2,386,047 Gates Oct. 2, 1945 2,402,736 Davis June 25, 1946 2,406,818 Erb Sept. 3, 1946 2,427,277 Hasselbaum Sept. 9, 1947 2,619,571 Ganci Nov. 25, 1952 FOREIGN PATENTS 605,675 Great Britain July 28, 1948 

